Some of the existing internal combustion engines are designed to use liquid petroleum gas (LPG) such as propane gas and butane gas for fuel. Such gas fuels generally have different calorific values or stoichiometric requirements, and are supplied at variously different pressures. The pressure of the gas that is actually delivered to the engine is controlled by a pressure regulator to a pressure that suits the particular gas fuel that is to be used.
It was proposed in Japanese patent laid open publication No. 2006-329041 (patent document 1) to provide a pair of metering jets that are configured for propane gas and butane gas, respectively, in a carburetor, and use a cam operated switching valve to conduct the gas fuel to one of the metering jets depending on the kind of the gas fuel that is being used.
This allows a single carburetor to be adapted to two different kinds of gas fuel simply by operating the switching valve. However, the carburetor is required to be equipped with a switching valve, two flow control valves and two metering jets. Therefore, the cost of the carburetor necessarily increases. Furthermore, the complexity and size of the carburetor increase, and this is highly undesirable particularly in small engines.